1. Technical Field
Embodiments disclosed herein relate generally to the field of near infrared measurement of absorbing components in a sample. More particularly, embodiments disclosed herein are related to measurement of Gas-Oil Ratio (GOR) for crude oil extraction.
2. Description of Related Art
The Gas-Oil Ratio (GOR) is an important parameter for practical purposes in oil extraction environments. GOR is a volumetric measure providing the ratio of gas to oil at atmospheric pressures, once the liquid is extracted from the “downhole” at high pressures. The GOR is conventionally defined as the volume of gas at standard conditions such as standard temperature and pressure conditions, in cubic feet divided by the number of stock tank barrels of oil (each stock tank barrel equal to 42 gallons). Stock tank refers to liquid at the surface, and not barrels of fluid at the reservoir. An inherent relation exists between GOR and the mass percentage of methane CH4 in the liquid at the downhole. A procedure to obtain GOR may be approximated by such methods described according to Mullins et al. “Gas-Oil Ratio of Live Crude Oils Determined by Near-Infrared Spectroscopy;” Appl. Spectrosc. 55(2) pp. 197-201. The relation between GOR and CH4 concentration in the downhole is valid for most crude oil samples having relatively low concentrations of H2S or CO2. Therefore, it is of practical importance to accurately measure CH4 dissolved in the liquid phase of the crude sample at the downhole.
Near-infrared (NIR) absorption spectroscopy has been used to estimate the GOR. Applications of NIR spectroscopy use one spectroscopic envelope located between 1620 and 1700 nm to estimate the GOR. Two absorption bands have been detected for CH4, one centered at 1670 nm, and one centered at 1682 nm. Also, there is knowledge of a CO2 absorption band centered at approximately 2010 nm. This has limited applications of NIR for measuring GOR to wavelengths below 2000 nm.
What is needed is a method to reliably determine components in a sample using broad-band absorption spectroscopy. More specifically, what is needed is a method to reliably determine GOR using broad band absorption spectroscopy.